This invention relates to video display systems and, more particularly, to improvements in the type of video display which employs a deformable material having deformations that depend upon a stored charge pattern and an optical subsystem for converting the deformations into a viewable image.
In recent years there have been developed techniques for displaying video information by storing a charge pattern representative of a video frame in a frame store and utilizing the charge pattern to modify a characteristic of a material. The modified characteristic of the material is then used to obtain a viewable image. For example, in my U.S. Pat. No. 3,882,271, there is disclosed an apparatus wherein a charge pattern on a special semiconductor frame store is used to obtain deformations of a deformable material disposed thereon. An optical subsystem, such as a Schleiren optical system, can then be utilized to convert the pattern of deformations (or "ripples") in the deformable material into a viewable image.
In other types of proposed systems, different media can be utilized for obtaining the viewable image. For example, in one such system the charge pattern can be used to control a liquid crystal material so that its light-reflecting properties are in a pattern that depends upon the stored charge pattern. In another such proposed system, the stored charge pattern can be used to control the amount of light output from electroluminescent media.
It is known in the video art that recursive filtering can be utilized to reduce noise in a video signal. In my U.S. Pat. No. 4,064,530, there is disclosed a digital video noise reduction system wherein a digital representation of the present instantaneous video signal is combined with a digital representation of video signal stored during previous frames to obtain a combined digital video signal that is converted back to analog form and ultimately displayed. The relative "weighting" of the present and previous signals that are combined at each instant (i.e., for each video pixel) is determined by a "motion detection" control signal. The motion detector portion of the system uses a digital comparator that is operative to compare the digital value (i.e., amplitude) of the present pixel with its counterpart in the stored video in order to determine the degree of "motion" at the particular position of the picture. If the new pixel value is close to the old pixel value, then little motion is attributed to this pixel of the image during the latest frame interval. In such case, the motion detector control signal operates to weight the above-referenced combination such that it includes a substantial fraction of the stored "old" picture information. For example, 3/4 of the previous frame signal may be combined with the unity complement fraction (i.e., 1/4), of the present "new" video signal. If, however, the motion detection operation reveals a relative dissimilarity between the old and new pixel values, significant "motion" is indicated at the particular position of the image being processed. In such case a motion detection signal is generated and used to more heavily weight the fraction of "new" video information contributed to forming the combined signal. For example, the fractions used may be 3/4 of "new" video signal to 1/4 "old" video signal. The overall noise reducer system thereby operates to eliminate noise most effectively from those portions of the image in which there is little or no motion. However, when motion is present in part of an image, the averaging in of old information would cause the appearance of "smearing" of the ultimately displayed video, so the noise reduction is automatically reduced or eliminated in those portions of the video field in which significant motion is detected.
It would be desirable to have a recursive filtering type of noise reduction system in most video receivers, but these units are typically expensive, and their cost has been a prohibitive factor with regard to consideration of employment of such noise reduction systems in relatively low cost television receivers or displays of the type that are most prevalent in home and office applications.
It is an object of the present invention to provide, at incrementally reasonable cost, a video noise reduction capability in the above-described type of video display wherein there already exists a means, such as a non-digital (analog) memory, for storing a frame of charge pattern.